1. Field of the Invention
The present invention relates to a personal authentication apparatus and personal authentication method, which can implement registration and a personal authentication method with high reproducibility.
2. Description of the Related Art
In recent years, interests and demands about the security technique are growing. There are some personal authentication methods that assure security. In a personal authentication system that uses a magnetic card such as a credit card or the like, or a contact type IC card with a built-in IC chip, a user must insert such card into a reader. When the user has his or her hands full with some pieces of baggage, the operation for inserting the card into the reader is troublesome and very inconvenient. In a personal authentication system that uses a non-contact type IC card represented by a commuter pass ticket examination system using a wireless communication, the user need not manually insert the card into a reader unlike the system that uses the contact type IC card. However, if the user loses his or her card, such card may be illicitly used as in the contact type. Also, the user must always carry the IC card.
By contrast, a personal authentication system that uses biometric information (biometrics) such as a fingerprint, iris, voice, face, and the like is known. In this system, the iris pattern of the user is registered in an authentication apparatus in advance, and is verified upon authentication. This authentication system can assure authentication precision 10 times as high as fingerprints. However, in order to assure high authentication precision, the eye must be irradiated with auxiliary light, and the user must bring his or her face into contact with an authentication apparatus. Hence, the system forces the user to take given authentication actions, and cannot assure user's hygiene. For this reason, such authentication system is used for only some limited users who require very high security. Recently, a non-contact authentication system which authenticates the user by sensing an image of the user's eye using a camera is available. However, in case of such non-contact system, since the image sensing condition of the user by the camera is unstable, sufficiently high authentication precision cannot be assured.
In a system that uses user's fingerprint information, the user touches a reader with his or her finger to sense its fingerprint, and can be authenticated by matching feature points. This system is unsusceptible to physical growth and aging as in the iris pattern. However, since the user's skin touches the contact surface of a detection device with his or her finger, the contact surface is contaminated with fat and sweat of the hand, and the precision deteriorates during use. Since the users directly touch the detection surface with fingers, some users may hate to use such system in terms of hygiene. If the hand of a person to be authenticated is dry, his or her finger cannot well contact the detection surface, and a fingerprint cannot be satisfactorily read.
In a personal authentication system using user's voice/utterance information, the authentication precision depends on user's physical conditions. For example, even the same person may often have lower voice reproducibility (e.g., a person may have a hoarse voice due to cold or hangover). For this reason, speaker recognition has a problem with its authentication precision, and has not been developed to a practical level.
In a personal authentication system that uses user's facial information, the user need not directly physically touch an authentication apparatus, and the user's facial image which is sensed by a camera need only be analyzed to authenticate that user. Therefore, compared to other systems, the load on the user can be lightened, and such system can be relatively easily used to open/close a gate. Such personal authentication system using user's facial information is described in, e.g., Jpn. Pat. KOKAI Publication Nos. 9-251534 and 11-175718.
In order to improve the authentication precision of the authentication system that utilizes a facial image, a facial image with a large information size must be sensed, and pixels equal to or larger than a predetermined value in number are required. However, when the height of the user is relatively higher than the camera position for image sensing or when the standing position of the user is far from the camera, a facial image to be sensed is small, the number of pixels of the facial image is also small and, hence, a given image information size cannot be assured, thus impairing the recognition precision. If the standing position of the user or the illumination condition of the image sensing site is different from that upon registration, i.e., the image sensing conditions between registration and authentication are largely different, the obtained image information varies, and personal authentication consequently fails.
If the user creates another facial expression upon sensing a facial image, the obtained facial pattern changes. Therefore, in order to improve the precision of personal authentication, various facial expressions must be registered upon registering a dictionary of a given user. Upon registering various facial expressions, if the user is strained, his or her expression looks stern. As a result, expected facial expressions cannot be registered, and a facial expression upon authentication becomes largely different from that upon registration, thus disturbing improvement in recognition precision. Conversely, if the system asks for user's cooperation to sense various facial expressions upon registering a dictionary, some users overreact, and a facial expression upon overreaction becomes largely different from that upon authentication.